JP4560479B2 - Manufacturing method of multimode optical interference device - Google Patents

Manufacturing method of multimode optical interference device Download PDF

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JP4560479B2
JP4560479B2 JP2005351802A JP2005351802A JP4560479B2 JP 4560479 B2 JP4560479 B2 JP 4560479B2 JP 2005351802 A JP2005351802 A JP 2005351802A JP 2005351802 A JP2005351802 A JP 2005351802A JP 4560479 B2 JP4560479 B2 JP 4560479B2
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JP2007156143A (en
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浩 和田
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Lapis Semiconductor Co Ltd
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Oki Semiconductor Co Ltd
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
    • G02B6/2808—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using a mixing element which evenly distributes an input signal over a number of outputs
    • G02B6/2813—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using a mixing element which evenly distributes an input signal over a number of outputs based on multimode interference effect, i.e. self-imaging

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Description

本発明は、光通信、光交換、光配線等で使用される多モード光干渉デバイス（Multi-Mode Interference device、以下「ＭＭＩ」という）の製造方法に関するものである。 The present invention relates to a method for manufacturing a multi-mode interference device (hereinafter referred to as “MMI”) used in optical communication, optical switching, optical wiring, and the like.

特開２００１−２１５４５２号公報Japanese Patent Laid-Open No. 2001-215542 米国特許第５５６３９６８号明細書US Pat. No. 5,563,968

図２（ａ），（ｂ）は、従来のＭＭＩの構造を示す平面図である。
例えば、図２（ａ）のＭＭＩは、光の導波路を形成する直方体の長手方向の一端に幅の狭いシングルモード導波路Ａ，Ｂを設け、他端にも幅の狭いシングルモード導波路Ｃ，Ｄを設けたものである。シングルモード導波路Ａ，Ｂと、シングルモード導波路Ｃ，Ｄの間は、幅の広いマルチモード導波路Ｍとなっている。また、シングルモード導波路Ａ，Ｂの間は、このシングルモード導波路Ａ，Ｂに対して垂直に端面Ｔ１が形成されている。また、シングルモード導波路Ｃ，Ｄの間は、このシングルモード導波路Ｃ，Ｄに対して垂直に端面Ｔ２が形成されている。 2 (a) and 2 (b) are plan views showing the structure of a conventional MMI.
For example, the MMI of FIG. 2A is provided with narrow single mode waveguides A and B at one end in the longitudinal direction of a rectangular parallelepiped forming an optical waveguide, and a narrow single mode waveguide C at the other end. , D are provided. A wide multimode waveguide M is formed between the single mode waveguides A and B and the single mode waveguides C and D. Further, between the single mode waveguides A and B, an end face T1 is formed perpendicular to the single mode waveguides A and B. Further, between the single mode waveguides C and D, an end face T2 is formed perpendicular to the single mode waveguides C and D.

このようなＭＭＩでは、シングルモード導波路Ａから入射された光は、幅の広いマルチモード導波路Ｍで複数のマルチモードに結合し、そのマルチモード間の干渉効果により、出射側のシングルモード導波路Ｃ，Ｄに分波されて出射される。これにより、分波器としての機能を果たす。また、シングルモード導波路Ａ，Ｂから、それぞれ異なる光を入射すると、これらの光が合波されてシングルモード導波路Ｃ，Ｄから出力されるという合波器としても機能する。   In such an MMI, the light incident from the single mode waveguide A is coupled to a plurality of multimodes by the wide multimode waveguide M, and the single-mode guide on the output side is caused by the interference effect between the multimodes. The light is demultiplexed into the waveguides C and D and emitted. This fulfills the function as a duplexer. In addition, when different lights are incident from the single mode waveguides A and B, they also function as a multiplexer in which these lights are combined and output from the single mode waveguides C and D.

しかしながら、図２（ａ）のＭＭＩでは、シングルモード導波路Ａから入射されてマルチモード導波路Ｍを通った光が、出射端の垂直な端面Ｔ２に当たって一部の光が反射してシングルモード導波路Ａに戻り、このシングルモード導波路Ａに接続された光源の特性に悪影響を与えることが知られている。   However, in the MMI of FIG. 2 (a), the light incident from the single mode waveguide A and passing through the multimode waveguide M hits the vertical end face T2 of the emission end, and a part of the light is reflected so Returning to the waveguide A, it is known that the characteristics of the light source connected to the single mode waveguide A are adversely affected.

一方、図２（ｂ）のＭＭＩは、前記特許文献２に記載されたもので、シングルモード導波路Ａ，Ｂの間の端面Ｔ１、及びシングルモード導波路Ｃ，Ｄの間の端面Ｔ２を、その導波路内で光軸に対して傾けることにより、この端面Ｔ２に当った光を導波路の平面内で角度を付けて反射させるようにし、反射光がシングルモード導波路Ａに直接戻らないように工夫を施している。   On the other hand, the MMI in FIG. 2B is described in Patent Document 2, and the end surface T1 between the single mode waveguides A and B and the end surface T2 between the single mode waveguides C and D are represented by By tilting with respect to the optical axis in the waveguide, the light hitting the end face T2 is reflected at an angle in the plane of the waveguide so that the reflected light does not return directly to the single mode waveguide A. Has been devised.

しかしながら、前記図２（ｂ）のＭＭＩでは、図２（ａ）のＭＭＩに比べて反射の影響は低減されるものの、出射側の端面Ｔ２で反射された光が、入射側の端面Ｔ１で再び反射されて出射側の端面Ｔ２に戻り、このような反射が導波路の平面内で繰り返される。そして、反射光の一部がシングルモード導波路Ａに戻ってしまう。このため、図２（ａ）のＭＭＩに比べて反射の影響は低減されるものの、反射光の影響を完全に無くすことができないという問題があった。   However, in the MMI of FIG. 2 (b), although the influence of reflection is reduced compared to the MMI of FIG. 2 (a), the light reflected by the end face T2 on the emission side is again reflected on the end face T1 on the incident side. Reflected and returned to the end face T2 on the exit side, such reflection is repeated in the plane of the waveguide. Then, a part of the reflected light returns to the single mode waveguide A. For this reason, although the influence of reflection is reduced as compared with the MMI of FIG. 2A, there is a problem that the influence of reflected light cannot be completely eliminated.

本発明は、簡単な構造で反射光の戻りを完全に除去することができるＭＭＩの製造方法を提供することを目的としている。 An object of the present invention is to provide a method of manufacturing an MMI that can completely remove the return of reflected light with a simple structure.

本発明は、マルチモード導波路の両端に単数または複数の幅の狭いシングルモード導波路を設け、入力側のシングルモード導波路から入射した光を前記マルチモード導波路で干渉させて出力側のシングルモード導波路から出射させる多モード光干渉デバイスの製造方法において、表面が結晶方向（０ １ １）と結晶方向（０ １ −１）で規定される平面となるように形成されたＩｎＰ結晶基板を下側クラッド層として、前記結晶基板上に導波路を構成するＩｎＧａＡｓＰ結晶による光導波路層、ＩｎＰ結晶による上側クラッド層、ＩｎＧａＡｓＰ結晶またはＩｎＧａＡｓ結晶によるキャップ層、及びエッチング用のＳｉＯIn the present invention, one or a plurality of narrow single mode waveguides are provided at both ends of the multimode waveguide, and light incident from the single mode waveguide on the input side is caused to interfere with the multimode waveguide to output a single mode on the output side. In a method for manufacturing a multimode optical interference device that emits light from a mode waveguide, an InP crystal substrate formed so that a surface is a plane defined by a crystal direction (0 1 1) and a crystal direction (0 1 -1) As a lower clad layer, an optical waveguide layer made of InGaAsP crystal constituting a waveguide on the crystal substrate, an upper clad layer made of InP crystal, a cap layer made of InGaAsP crystal or InGaAs crystal, and SiO2 for etching ２2 によるマスク層を順次形成する工程と、前記マスク層と前記キャップ層とをパターニングし、前記マルチモード導波路と前記シングルモード導波路の方向が前記結晶基板の前記結晶方向（０ １ １）に一致するようにマスクパターンを形成する工程と、前記マスクパターンをマスクとして、ＩｎＧａＡｓＰはエッチングせずＩｎＰのみをエッチングする選択エッチング液を用いて、前記光導波路層はエッチングせず前記上側クラッド層のみをエッチングし、前記マルチモード導波路の両端で前記シングルモード導波路が設けられていない壁面が、前記上側クラッド層の結晶面に沿って前記結晶基板の表面に対して約５４．８°をなすように形成する工程と、前記マスクパターンをマスクとして前記上側クラッド層、前記光導波路層、及び前記結晶基板をドライエッチングし、前記光導波路層の壁面が前記結晶基板の表面に対して約５４．８°を維持した状態で所定の厚さだけ垂直方向に除去する工程とを順次行うことを特徴としている。Forming a mask layer in sequence, patterning the mask layer and the cap layer, and the directions of the multimode waveguide and the single mode waveguide coincide with the crystal direction (0 1 1) of the crystal substrate Forming a mask pattern, and using the mask pattern as a mask, using a selective etchant that etches only InP without etching InGaAsP, and etches only the upper cladding layer without etching the optical waveguide layer. The wall surfaces where the single mode waveguide is not provided at both ends of the multimode waveguide form an angle of about 54.8 ° with respect to the surface of the crystal substrate along the crystal plane of the upper cladding layer. Forming the upper clad layer, the optical waveguide layer, and the mask pattern as a mask; and A step of performing dry etching of the crystal substrate and sequentially removing a predetermined thickness in a vertical direction while maintaining a wall surface of the optical waveguide layer at about 54.8 ° with respect to the surface of the crystal substrate. It is said.

本発明によって製造されたＭＭＩでは、マルチモード導波路の両端でシングルモード導波路が設けられていない光軸方向に垂直な壁面が、基板の表面に対し約５４．８°の傾斜を有している。これにより、一部の光が基板の表面に対して約５４．８°の傾斜面を形成する壁面で反射される。反射された光は、基板の表面に向かって進むが、この基板に対する入射角が小さいため、ほとんどの光は基板の表面で反射されずに基板内に放射される。従って、壁面で反射された光が、導波路に戻るおそれがなくなる。従って、簡単な構造で反射光の戻りを完全に除去することができるという効果がある。 In the MMI manufactured according to the present invention, the wall surface perpendicular to the optical axis direction where the single mode waveguide is not provided at both ends of the multimode waveguide has an inclination of about 54.8 ° with respect to the surface of the substrate. Yes. Thereby, a part of light is reflected by the wall surface forming an inclined surface of about 54.8 ° with respect to the surface of the substrate. The reflected light travels toward the surface of the substrate, but since the incident angle with respect to the substrate is small, most of the light is radiated into the substrate without being reflected by the surface of the substrate. Therefore, there is no possibility that the light reflected by the wall surface returns to the waveguide. Therefore, there is an effect that the return of the reflected light can be completely removed with a simple structure.

このＭＭＩの製造は次のような工程で行うことができる。
まず、表面が結晶方向（０ １ １）と結晶方向（０ １ −１）で規定される平面となるように形成されたＩｎＰ結晶基板を下側クラッド層として、前記結晶基板上に導波路を構成するＩｎＧａＡｓＰ結晶による光導波路層、ＩｎＰ結晶による上側クラッド層、ＩｎＧａＡｓＰ結晶またはＩｎＧａＡｓ結晶によるキャップ層、及びエッチング用のＳｉＯ２によるマスク層を順次形成する。次に、前記マスク層と前記キャップ層とをパターニングして前記マルチモード導波路と前記シングルモード導波路の方向が前記結晶基板の前記結晶方向（０ １ １）に一致するようにマスクパターンを形成する。次に、前記マスクパターンをマスクとして、ＩｎＧａＡｓＰはエッチングせずＩｎＰのみをエッチングする選択エッチング液を用いて、前記光導波路層はエッチングせず前記上側クラッド層のみをエッチングし、前記マルチモード導波路の両端で前記シングルモード導波路が設けられていない壁面が、前記上側クラッド層の結晶面に沿って前記結晶基板の表面に対して約５４．８°をなすように形成する。そして、前記マスクパターンをマスクとして前記上側クラッド層、前記光導波路層、及び前記結晶基板をドライエッチングし、前記光導波路層の壁面が前記結晶基板の表面に対して約５４．８°を維持した状態で所定の厚さだけ垂直方向に除去する。 This MMI can be manufactured by the following steps.
First, an InP crystal substrate formed so that the surface is a plane defined by a crystal direction (0 1 1) and a crystal direction (0 1 -1) is used as a lower cladding layer, and a waveguide is formed on the crystal substrate. An optical waveguide layer made of InGaAsP crystal, an upper cladding layer made of InP crystal, a cap layer made of InGaAsP crystal or InGaAs crystal, and a mask layer made of SiO 2 for etching are sequentially formed. Next, the mask layer and the cap layer are patterned to form a mask pattern so that the directions of the multimode waveguide and the single mode waveguide coincide with the crystal direction (0 1 1) of the crystal substrate. To do. Next, using the mask pattern as a mask, a selective etchant that etches only InP without etching InGaAsP, etches only the upper cladding layer without etching the optical waveguide layer, and forms the multimode waveguide. The wall surface where the single mode waveguide is not provided at both ends is formed so as to form about 54.8 ° with respect to the surface of the crystal substrate along the crystal plane of the upper clad layer. Then, the upper cladding layer, the optical waveguide layer, and the crystal substrate were dry-etched using the mask pattern as a mask, and the wall surface of the optical waveguide layer was maintained at about 54.8 ° with respect to the surface of the crystal substrate . In the state, a predetermined thickness is removed in the vertical direction.

この発明の前記並びにその他の目的と新規な特徴は、次の好ましい実施例の説明を添付図面と照らし合わせて読むと、より完全に明らかになるであろう。但し、図面は、もっぱら解説のためのものであって、この発明の範囲を限定するものではない。   The above and other objects and novel features of the present invention will become more fully apparent when the following description of the preferred embodiment is read in conjunction with the accompanying drawings. However, the drawings are for explanation only, and do not limit the scope of the present invention.

図１（ａ）〜（ｃ）は、本発明の実施例を示すＭＭＩの構成図であり、同図（ａ）は斜視図、同図（ｂ）は同図（ａ）中のＸ１−Ｘ２に沿う部分の断面図、及び同図（ｃ）は同図（ａ）中のＹ１−Ｙ２に沿う部分の断面図である。   1A to 1C are configuration diagrams of an MMI showing an embodiment of the present invention, where FIG. 1A is a perspective view, and FIG. 1B is X1-X2 in FIG. 1A. Sectional drawing of the part which follows this, and the figure (c) are sectional drawings of the part which follows Y1-Y2 in the figure (a).

このＭＭＩは、下側のクラッド層となるＩｎＰ結晶による基板１の上に、厚さ０．５μｍ程度のＩｎＧａＡｓＰ結晶によって導波路を構成する光導波層２と、厚さ２〜４μｍ程度のＩｎＰ結晶による上側のクラッド層３を順次積層し、これを長さが１００〜５００μｍで、幅が１５〜１００μｍ程度のほぼ直方体の形状に加工して形成したものである。   This MMI is composed of an optical waveguide layer 2 having a waveguide formed of an InGaAsP crystal having a thickness of about 0.5 μm and an InP crystal having a thickness of about 2 to 4 μm on a substrate 1 made of InP crystal serving as a lower cladding layer. The upper clad layer 3 is sequentially laminated and processed into a substantially rectangular parallelepiped shape having a length of 100 to 500 μm and a width of about 15 to 100 μm.

図１（ａ）に示すように、直方体のＸＹ表面は、Ｘ軸方向が結晶方向（０ １ １）、Ｙ軸方向が結晶方向（０ １ −１）で規定される面に一致するように設定され、この直方体の長手方向であるＸ軸方向、即ち導波路の方向は、結晶方向（０ １ １）となるように設定されている。   As shown in FIG. 1 (a), the XY surface of the rectangular parallelepiped coincides with the plane defined by the crystal direction (0 1 1) in the X-axis direction and the crystal direction (0 1 -1) in the Y-axis direction. The X-axis direction that is the longitudinal direction of the rectangular parallelepiped, that is, the direction of the waveguide is set to be the crystal direction (0 1 1).

導波路の中央部は、直方体のＹ軸方向の幅全体で構成されるマルチモード導波路Ｍとなっている。導波路の一端には、マルチモード導波路Ｍの中央部を削除して形成された端面Ｔ１が設けられ、この端面Ｔ１の両側に残された導波路がシングルモード導波路Ａ，Ｂとなっている。シングルモード導波路Ａ，Ｂの幅は光の波長とほぼ同じ２μｍ程度に形成され、長さは１０μｍ程度またはそれ以上となっている。一方、シングルモード導波路Ａ，Ｂの間に設けられた端面Ｔ１は、基板１の表面に対して約５４．８°の角度θとなるように斜めに形成されている。即ち、この端面Ｔ１は、光軸方向に垂直な壁面が、厚さ方向に傾斜を付けられて形成されている。   The central portion of the waveguide is a multimode waveguide M configured by the entire width of the rectangular parallelepiped in the Y-axis direction. One end of the waveguide is provided with an end face T1 formed by deleting the central portion of the multimode waveguide M, and the waveguides left on both sides of the end face T1 become single mode waveguides A and B. Yes. The widths of the single mode waveguides A and B are formed to be about 2 μm which is substantially the same as the wavelength of light, and the length is about 10 μm or more. On the other hand, the end face T1 provided between the single mode waveguides A and B is formed obliquely with respect to the surface of the substrate 1 so as to have an angle θ of about 54.8 °. That is, the end face T1 is formed by inclining the wall surface perpendicular to the optical axis direction in the thickness direction.

また、導波路の他端にも、シングルモード導波路Ａ，Ｂ及び端面Ｔ１に対して対称となるように、シングルモード導波路Ｃ，Ｄ及び端面Ｔ２が形成されている。   Also, the single mode waveguides C and D and the end face T2 are formed at the other end of the waveguide so as to be symmetric with respect to the single mode waveguides A and B and the end face T1.

図３は、図１のＭＭＩの製造方法を示す工程図である。なお、この工程図の各工程における右側の断面図は図１（ｂ）のＸ１−Ｘ２断面に対応し、左側の断面図は図１（ｃ）のＹ１−Ｙ２断面に対応するものである。以下、この図３を参照しつつ、図１のＭＭＩの製造方法を説明する。   FIG. 3 is a process diagram showing a method of manufacturing the MMI of FIG. In addition, the right side cross-sectional view in each step of this process diagram corresponds to the X1-X2 cross section of FIG. 1B, and the left cross-sectional view corresponds to the Y1-Y2 cross section of FIG. Hereinafter, a method of manufacturing the MMI of FIG. 1 will be described with reference to FIG.

（１） 工程１
表面が結晶方向（０ １ １）と結晶方向（０ １ −１）で規定される平面となるように形成されたＩｎＰ結晶による基板１を準備し、この基板１の表面に、図３（ａ）に示すように、導波路を構成する厚さ０．５μｍ程度のＩｎＧａＡｓＰ結晶による光導波層２と、厚さ２〜４μｍ程度のＩｎＰ結晶によるクラッド層３と、後のウェットエッチングでマスクとして使用するＩｎＧａＡｓＰ結晶またはＩｎＧａＡｓ結晶によるキャップ層４と、ＳｉＯ２によるマスク層５を、順次形成する。 (1) Process 1
A substrate 1 made of an InP crystal formed so that the surface is a plane defined by a crystal direction (0 1 1) and a crystal direction (0 1 -1) is prepared. ), The optical waveguide layer 2 made of an InGaAsP crystal having a thickness of about 0.5 μm, the cladding layer 3 made of an InP crystal having a thickness of about 2 to 4 μm, and used as a mask in subsequent wet etching, as shown in FIG. A cap layer 4 made of InGaAsP crystal or InGaAs crystal and a mask layer 5 made of SiO 2 are sequentially formed.

（２） 工程２
通常のホトリソグラフィ技術と、Ｃｌ２とＡｒの混合ガスを用いたリアクティブ・イオン・エッチング技術を使用して、マスク層５とキャップ層４をエッチングし、図３（ｂ）に示すように、これらのマスク層５とキャップ層４によるマスクパターンＭＳＫを形成する。なお、図３中にマスクパターンＭＳＫの平面図は記載されていないが、図１（ａ）のクラッド層３の表面と同じ形状である。このとき、マスクパターンＭＳＫのＸ軸方向は、結晶方向（０ １ １）に一致するように設定する。 (2) Process 2
The mask layer 5 and the cap layer 4 are etched using a normal photolithography technique and a reactive ion etching technique using a mixed gas of Cl 2 and Ar, as shown in FIG. A mask pattern MSK is formed by the mask layer 5 and the cap layer 4. In addition, although the top view of mask pattern MSK is not described in FIG. 3, it is the same shape as the surface of the clad layer 3 of FIG. At this time, the X-axis direction of the mask pattern MSK is set to coincide with the crystal direction (0 1 1).

（３） 工程３
マスクパターンＭＳＫをエッチングマスクとして、ＩｎＧａＡｓＰはエッチングせずにＩｎＰのみをエッチングするＨＣｌ等の選択エッチング液を用い、選択ウェットエッチングを行う。この選択ウェットエッチングでは、クラッド層３のＩｎＰが、結晶面に沿ってエッチングされる。従って、図３（ｃ）に示すように、クラッド層３のＸ１−Ｘ２断面は結晶面に一致し、基板１の表面に対して約５４．８°の傾斜面となる。一方、クラッド層３のＹ１−Ｙ２断面は、垂直に形成される。また、クラッド層３の下側のＩｎＧａＡｓＰによる光導波層２は、エッチングされずに、そのまま残る。なお、マスクパターンＭＳＫを構成するキャップ層４は、クラッド層３との密着性が良いので、選択エッチング液がマスクパターンＭＳＫとクラッド層３の間に浸入することによるサイドエッチを防止する効果がある。 (3) Process 3
Using the mask pattern MSK as an etching mask, selective wet etching is performed using a selective etching solution such as HCl that etches only InP without etching InGaAsP. In this selective wet etching, InP of the cladding layer 3 is etched along the crystal plane. Therefore, as shown in FIG. 3C, the X1-X2 cross section of the clad layer 3 coincides with the crystal plane, and becomes an inclined surface of about 54.8 ° with respect to the surface of the substrate 1. On the other hand, the Y1-Y2 cross section of the cladding layer 3 is formed vertically. Further, the optical waveguide layer 2 made of InGaAsP below the cladding layer 3 is left without being etched. Note that the cap layer 4 constituting the mask pattern MSK has good adhesion to the cladding layer 3, and therefore has an effect of preventing side etching due to the selective etchant entering between the mask pattern MSK and the cladding layer 3. .

（４） 工程４
選択ウェットエッチングの後、再び、Ｃｌ２とＡｒの混合ガスを用いたリアクティブ・イオン・エッチングを施す。これにより、図３（ｃ）の断面形状を保ったまま垂直にエッチングが進み、クラッド層３と、光導波層２と、基板１が同じ厚さだけ均一にエッチングされて除去される。基板１の表面が１〜３μｍ程度エッチングされた時点で、エッチングを停止する。これにより、クラッド層３の下側と、光導波層２と、基板１の一部のＸ１−Ｘ２断面が、この基板１の表面に対して約５４．８°の傾斜面となる。また、光導波層２と基板１のＹ１−Ｙ２断面は、垂直に形成される。これにより、図３（ｄ）に示す形状のＭＭＩが形成される。この後、マスクパターンＭＳＫを除去することによって、図１に示すようなＭＭＩが完成する。 (4) Process 4
After selective wet etching, reactive ion etching using a mixed gas of Cl 2 and Ar is performed again. Thereby, the etching proceeds vertically while maintaining the cross-sectional shape of FIG. 3C, and the cladding layer 3, the optical waveguide layer 2, and the substrate 1 are uniformly etched by the same thickness and removed. The etching is stopped when the surface of the substrate 1 is etched by about 1 to 3 μm. Thereby, the X1-X2 cross section of the lower side of the cladding layer 3, the optical waveguide layer 2, and a part of the substrate 1 becomes an inclined surface of about 54.8 ° with respect to the surface of the substrate 1. Moreover, the Y1-Y2 cross section of the optical waveguide layer 2 and the substrate 1 is formed vertically. As a result, the MMI having the shape shown in FIG. Thereafter, the MMI as shown in FIG. 1 is completed by removing the mask pattern MSK.

このＭＭＩでは、例えば分波器として使用する場合、光ファイバで導かれた光やレーザダイオードから出力された光等を、レンズを介してシングルモード導波路Ａに入射する。屈折率がほぼ３．５の光導波層２に入射された光は、この光導波層２を挟む屈折率がほぼ３．１の基板１とクラッド層３との間で全反射されながら、この光導波層２中を進む。そして、幅の広いマルチモード導波路Ｍで複数のマルチモードに結合し、そのマルチモード間の干渉効果により、出射側のシングルモード導波路Ｃ，Ｄに分波されて出射される。この時、一部の光は、基板１の表面に対して約５４．８°の傾斜面を形成する端面Ｔ２で反射される。反射された光は、基板１の表面に向かって進むが、この基板１に対する入射角が小さいため、ほとんどの光は基板１の表面で反射されずに基板１内に放射される。従って、端面Ｔ２で反射された光が、シングルモード導波路Ａに戻るおそれがなくなる。   In this MMI, for example, when used as a duplexer, light guided by an optical fiber, light output from a laser diode, or the like enters the single mode waveguide A through a lens. The light incident on the optical waveguide layer 2 having a refractive index of approximately 3.5 is totally reflected between the substrate 1 having a refractive index of approximately 3.1 and the clad layer 3 sandwiching the optical waveguide layer 2. Proceeds through the optical waveguide layer 2. Then, the multimode waveguide M having a wide width is coupled to a plurality of multimodes, and is demultiplexed and emitted to the single-mode waveguides C and D on the emission side by the interference effect between the multimodes. At this time, a part of the light is reflected by the end face T <b> 2 that forms an inclined surface of about 54.8 ° with respect to the surface of the substrate 1. The reflected light travels toward the surface of the substrate 1, but since the incident angle with respect to the substrate 1 is small, most of the light is radiated into the substrate 1 without being reflected by the surface of the substrate 1. Therefore, there is no possibility that the light reflected by the end face T2 returns to the single mode waveguide A.

また、このＭＭＩは、例えばシングルモード導波路Ａ，Ｂから、それぞれ異なる光を入射し、マルチモード導波路Ｍでこれらの光を合波してシングルモード導波路Ｃ，Ｄから出力する合波器としても使用することができる。この場合も、端面Ｔ２で反射された光が、シングルモード導波路Ａ，Ｂに戻るおそれはない。   In addition, this MMI is, for example, a multiplexer that receives different light beams from the single mode waveguides A and B, multiplexes these lights in the multimode waveguide M, and outputs them from the single mode waveguides C and D. Can also be used. Also in this case, there is no possibility that the light reflected by the end face T2 returns to the single mode waveguides A and B.

このように、本実施例のＭＭＩは、基板１の表面に対して傾斜面を有する端面Ｔ１，Ｔ２を有しているので、これらの端面Ｔ１，Ｔ２で反射された光は基板１を通して外部に放射され、シングルモード導波路Ａ，Ｂに光が戻って光源の特性に悪影響を与えるおそれがないという利点がある。   As described above, the MMI of the present embodiment has the end surfaces T1 and T2 having inclined surfaces with respect to the surface of the substrate 1, so that the light reflected by these end surfaces T1 and T2 is transmitted to the outside through the substrate 1. There is an advantage that there is no possibility that the light is radiated and the light returns to the single mode waveguides A and B to adversely affect the characteristics of the light source.

また、傾斜面を有する端面Ｔ１，Ｔ２は、基板１、光導波層２及びクラッド層３を構成するＩｎＰ結晶の特性を利用したエッチングによって形成しているので、複雑な工程を必要とせず、簡単に傾斜面を形成することができるという利点がある。   Further, the end surfaces T1 and T2 having inclined surfaces are formed by etching utilizing the characteristics of the InP crystals constituting the substrate 1, the optical waveguide layer 2 and the cladding layer 3, so that a complicated process is not required and simple. There is an advantage that an inclined surface can be formed.

なお、上記実施例で示した寸法や材料は一例であり、適用するＭＭＩに応じて任意の寸法や材料を使用することができる。   Note that the dimensions and materials shown in the above embodiments are examples, and arbitrary dimensions and materials can be used according to the applied MMI.

また、構造も図示したものに限定されない。即ち、マルチモード導波路Ｍの両側に設けられるシングルモード導波路の数は、それぞれ２個ずつに限定されない。例えば、３分岐の場合は、入射側に１個、出射側に３個を設けて構成することができる。   Further, the structure is not limited to the illustrated one. That is, the number of single mode waveguides provided on both sides of the multimode waveguide M is not limited to two each. For example, in the case of three branches, one can be provided on the incident side and three can be provided on the emission side.

本発明の実施例を示すＭＭＩの構成図である。It is a block diagram of MMI which shows the Example of this invention. 従来のＭＭＩの構造を示す平面図である。It is a top view which shows the structure of the conventional MMI. 図１のＭＭＩの製造方法を示す工程図である。It is process drawing which shows the manufacturing method of MMI of FIG.

符号の説明Explanation of symbols

１ 基板
２ 光導波層
３ クラッド層
４ キャップ層
５ マスク層
Ａ，Ｂ，Ｃ，Ｄ シングルモード導波路
Ｍ マルチモード導波路
Ｔ１，Ｔ２ 端面 1 substrate 2 optical waveguide layer 3 clad layer 4 cap layer 5 mask layer A, B, C, D single mode waveguide M multimode waveguide T1, T2 end face

Claims (3)

マルチモード導波路の両端に単数または複数の幅の狭いシングルモード導波路を設け、入力側のシングルモード導波路から入射した光を前記マルチモード導波路で干渉させて出力側のシングルモード導波路から出射させる多モード光干渉デバイスの製造方法において、Single or multiple narrow single-mode waveguides are provided at both ends of the multi-mode waveguide, and light incident from the input-side single-mode waveguide is caused to interfere with the multi-mode waveguide from the output-side single-mode waveguide. In the manufacturing method of the multimode optical interference device to emit,
表面が結晶方向（０ １ １）と結晶方向（０ １ −１）で規定される平面となるように形成されたＩｎＰ結晶基板を下側クラッド層として、前記結晶基板上に導波路を構成するＩｎＧａＡｓＰ結晶による光導波路層、ＩｎＰ結晶による上側クラッド層、ＩｎＧａＡｓＰ結晶またはＩｎＧａＡｓ結晶によるキャップ層、及びエッチング用のＳｉＯA waveguide is formed on the crystal substrate with the InP crystal substrate formed so that the surface becomes a plane defined by the crystal direction (0 1 1) and the crystal direction (0 1 -1) as a lower clad layer. Optical waveguide layer made of InGaAsP crystal, upper cladding layer made of InP crystal, cap layer made of InGaAsP crystal or InGaAs crystal, and SiO for etching ２2 によるマスク層を順次形成する工程と、Sequentially forming a mask layer by
前記マスク層と前記キャップ層とをパターニングし、前記マルチモード導波路と前記シングルモード導波路の方向が前記結晶基板の前記結晶方向（０ １ １）に一致するようにマスクパターンを形成する工程と、Patterning the mask layer and the cap layer, and forming a mask pattern so that directions of the multimode waveguide and the single mode waveguide coincide with the crystal direction (0 1 1) of the crystal substrate; ,
前記マスクパターンをマスクとして、ＩｎＧａＡｓＰはエッチングせずＩｎＰのみをエッチングする選択エッチング液を用いて、前記光導波路層はエッチングせず前記上側クラッド層のみをエッチングし、前記マルチモード導波路の両端で前記シングルモード導波路が設けられていない壁面が、前記上側クラッド層の結晶面に沿って前記結晶基板の表面に対して約５４．８°をなすように形成する工程と、Using the mask pattern as a mask, a selective etchant that etches only InP without etching InGaAsP, etches only the upper cladding layer without etching the optical waveguide layer, and at both ends of the multimode waveguide Forming a wall surface not provided with a single mode waveguide so as to form about 54.8 ° with respect to the surface of the crystal substrate along the crystal plane of the upper clad layer;
前記マスクパターンをマスクとして前記上側クラッド層、前記光導波路層、及び前記結晶基板をドライエッチングし、前記光導波路層の壁面が前記結晶基板の表面に対して約５４．８°を維持した状態で所定の厚さだけ垂直方向に除去する工程とを、Using the mask pattern as a mask, the upper cladding layer, the optical waveguide layer, and the crystal substrate are dry etched, and the wall surface of the optical waveguide layer is maintained at about 54.8 ° with respect to the surface of the crystal substrate. Removing a predetermined thickness in the vertical direction,
順次行うことを特徴とする多モード光干渉デバイスの製造方法。A method of manufacturing a multimode optical interference device, which is performed sequentially. 前記光導波路層は、厚さ０．５μｍ程度のＩｎＧａＡｓＰ結晶であり、The optical waveguide layer is an InGaAsP crystal having a thickness of about 0.5 μm,
前記上側クラッド層は、厚さ２〜４μｍ程度のＩｎＰ結晶であることを特徴とする請求項１記載の多モード光干渉デバイスの製造方法。2. The method of manufacturing a multimode optical interference device according to claim 1, wherein the upper clad layer is an InP crystal having a thickness of about 2 to 4 [mu] m. 前記選択エッチング液は、ＨＣｌであることを特徴とする請求項１又は２に記載の多モード光干渉デバイスの製造方法。The method for manufacturing a multimode optical interference device according to claim 1, wherein the selective etching solution is HCl.
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